The invention relates to a valve assembly, and more particularly a valve assembly for a tank to prevent the overfilling of a tank.
There have been a number of valves developed to prevent the fluid level in tanks from exceeding a predetermined level. When using tanks filled with compressed or liquified gas, such as propane, it is important that the compressed or liquified gas not exceed a certain fluid level in the tank so that a sufficient amount of head space at the top of the tank is maintained for safety purposes. Due to the high co-efficient of thermal expansion of many liquified gases, an increase in ambient temperature can cause the head space in the tank to be rapidly consumed. These tanks are rated so as to withstand a predetermined amount of internal pressure; however, if the tank is overfilled beyond the maximum level, there is a danger that the internal pressure may exceed the rated strength of the tank which could lead to a failure in the tank.
Many devices have been designed to avoid overfilling of such tanks. One such device includes the use of a dip tube that extends through the tank wall to a specific level below the maximum fluid level such that one end of the tube is open to atmosphere. Thus, once the fluid level in the tank reaches the bottom end of the tube, the liquified gas is evacuated from the tank. Other devices that have been used incorporate the use of a primary valve member and a secondary valve member controlled by a float assembly. The primary valve blocks incoming fluid flow when the flow assembly is operable at maximum fluid conditions to seat the secondary valve. When the secondary valve seals its associated port, there is a fluid pressure build up between the secondary and primary valve that pushes the primary valve into its seat sealing lateral ports to stop fluid flow into the tank. Another type of float device as disclosed in U.S. Pat. No. 6,076,546 to Waters, includes a valve member which shifts in a valve housing controlled by the rising-and falling of a float assembly as the fluid level in the vessel rises and falls. The valve member shifts into a blocking position relative to a port in the housing that communicates with the tank interior at a predetermined maximum fluid level in the interior space. When the fluid level in the tank is below the maximum fluid level, the float assembly shifts the valve member from the blocking position and keeps it removed from the flow of fluid between the flow path and the port. Recently, new regulations have been drafted which require the overfill valve to prevent further filling of the tank until the tank is emptied of fluid. Specifically UL 2227 dated Nov. 19, 1999, which is incorporated herein by reference, requires that LP-Gas container, after initially being shut off, shall not reopen to grant an increase of more than two percent when test at pressures of 15 psig and 125 psig. Prior valves have prevented overfilling the tank once a maximum liquid level has been reached; however the valves allow refilling of the tank once the liquid level in the tank has dropped below the maximum liquid. Accordingly, there is a need for a simple, inexpensive valve which prevents the overfilling of tanks beyond a predetermined level in the tank and also prevents refilling the tank until the fluid in the tank has been substantially evacuated from the interior of the tank, and which complies with present day overfilling requirements.
In accordance with the principal aspect of the present invention, a valve assembly is provided which prevents fluid flow into a vessel, such as an LP tank, once a predetermined maximum fluid level in the tank has been reached. In one embodiment, the valve assembly is also designed to prevent further filling of the tank after a predetermined maximum fluid level in the tank has been reached until after the fluid level has dropped to a predetermined lower liquid level and the supply pressure to the valve assembly has dropped below a predetermined pressure. In one specific embodiment, the predetermined lower liquid level is the level of the liquid in the tank when the tank is empty or substantially empty of all fluid. Such a predetermined lower liquid level is typically selected for highly volatile liquids. Highly volatile liquids are defined as liquids having a boiling point of less than about 100xc2x0 F. Such liquids include, but not limited to, butane, hydrogen, oxygen, propane, and the like. As can be appreciated, a tank including a non-highly volatile liquid can also have the predetermined lower liquid level set for a level at which the liquid in the tank is empty or substantially empty of all fluid. As can also be appreciated, tanks that contain highly volatile liquids can have the predetermined lower liquid level set at a low level when the liquid in the tank is not completely empty of all fluid. With further regard to this embodiment, the valve assembly prevents filling of the tank after the predetermined lower fluid level in the tank has been reached until the supply pressure in the valve assembly has dropped to atmospheric pressure, namely 14.7 psi. The atmospheric pressure level is preferred for highly volatile liquids, but a tank including a non-highly volatile liquid can also have atmospheric pressure as the predetermined lower inlet pressure level for the valve assembly to open and allow filling of the tank. As can also be appreciated, valve assemblies for tanks that contain highly volatile liquids can have the predetermined lower pressure level set at a pressure above atmospheric pressure. The valve assembly is particularly designed for use with liquified gas tanks such as, but not limited to, LP tanks.
A primary object of the present invention is the provision of a safety valve that prevents the overfilling of a tank with liquid under pressure.
Another object of the invention is the provision of a safety valve that prevents further filling of a tank once a predetermined maximum fluid level is reached in the tank during filling of the tank.
Still another object of the invention is the provision of a safety valve that prevents refilling of the tank once a predetermined maximum fluid level is obtained in the tank until after the supply pressure to the valve is reduced to a predetermined low pressure.
Still another object of the invention is the provision of a safety valve for use on LP tanks.
A further object of the invention is the provision of a safety valve that allows for rapid filling of the tank.
Still another object of the invention is the provision of a safety valve which is economical to produce and efficient and reliable in operation.